A hybrid vehicle comprises an internal combustion heat engine, which transmits the driving torque to the driving wheels through a transmission provided with a gearbox, and at least one electric machine which is mechanically connected to the driving wheels and is electrically connected to a system for the storage of electric energy. Normally, the system for the storage of electric energy comprises a pack of chemical batteries which are connected to each other in series and in parallel.
The placement of the storage system into the vehicle may be very complex, particularly in the case of a high performance sports vehicle which has very small inside spaces. In particular, the storage system must be possibly arranged close to the electric machine to reduce the length of the electric connection cables (i.e. to reduce the weight of the electric cables and the power losses by Joule effect in the electric cables themselves), must be possibly arranged in a position protected from crashes, must be arranged in a position protected from heat sources and that can be easily cooled down as it cannot withstand high temperatures, and must be arranged so as not to unbalance the vehicle balance with its relevant mass (in other words, it must be arranged centrally close to the barycenter and must be arranged close to the ground to obtain a good dynamic behavior of the vehicle).
It has been proposed to arrange the batteries of the storage system at the floor that makes up a bottom wall of the compartment (i.e. lie the storage system on the floor or insert the storage system into the box-shaped floor). The arrangement of the storage system at the floor offers several advantages, since in this way the storage system is highly protected against crashes being arranged into the safety cell of the compartment, is relatively close to the electric machine, is arranged in a position not subject to overheating and is easy to be cooled down, and is arranged very close to the ground in central position.
However, the useful height for the storage system at the floor is reduced (approximately in the order of few centimeters), particularly in the case of a high performance sports vehicle having a very small overall height from the ground. Accordingly, in order to arrange the storage system at the floor, the chemical batteries of the storage system must have a very small overall thickness; thus, the traditional chemical batteries for motor traction which have a shape similar to the cubic shape (i.e. they have a relevant thickness which is equal to if not higher than, the width/length) are not suitable to be arranged at the floor.
Patent application DE102007010742A1 and patent application DE102007010748A1 describe a system for the storage of electric energy for a vehicle comprising a pack of chemical batteries, which are connected to each other in series and in parallel and comprise respective electrochemical cells; each chemical battery has a cylindrical shape having a central (longitudinal) symmetry axis. The chemical batteries are arranged into a parallelepiped container, are vertically oriented and lie on a lower cooling plate which serves as a support base; a plurality of heat conductive bar perpendicularly raise from the cooling plate which bars are arranged between the chemical batteries. The free spaces between the chemical batteries 2 are filled with a plastic substance (in particular, an epoxy resin, polyurethane or silicone) which leaves only the upper part of the chemical batteries exposed at the electric terminals.
Patent application US2012003508A1 describes a system for the storage of electric energy for a vehicle comprising a pack of chemical batteries, which are connected to each other in series and in parallel and comprise respective electrochemical cells. Each chemical battery has a cylindrical shape having a central (longitudinal) symmetry axis. The chemical batteries are arranged into a parallelepiped container, are vertically oriented and lie on a lower cooling plate which serves as a support base. The free spaces between the chemical batteries are filled with a plastic substance (in particular, an electrically insulating foam) which leaves an upper part of the chemical batteries exposed at the electric terminals.